Grafting Method By Means of Ionising Radiation Using a Reactive Surfactant Molecule, Textile Substrate and Battery Separator Obtained by Means of Grafting

ABSTRACT

A method for grafting functional chemical groups to a textile substrate is provided, wherein the substrate is impregnated with a solution of a functional molecule, containing the functional chemical group and a group that is reactive to ionising radiation, as well as a surfactant molecule that can improve the wettability of the textile substrate by the solution. The surfactant molecule contains at least two types of groups that are reactive to ionising radiation. Subsequently, ionising radiation is applied to the impregnated textile substrate and the reaction of the reactive groups bridge-grafts the functional molecules to the surfactant molecules. A textile substrate and a battery separator grafted using the above method are also described.

BACKGROUND Field of the Invention

The invention relates to a method for grafting functional chemical groups on a textile substrate, and a textile substrate and battery separator grafted using such a method.

The invention particularly applies to the grafting of textile substrates so as to give them an ion exchange function. In particular, the invention proposes a method for grafting a bipolar textile substrate, i.e. comprising a different ion exchange function on each of the faces thereof.

The grafted textile substrates according to the invention are particularly useful in the agri-food, pharmaceutical, medical, energy, biological and environmental sectors. For example, the use of ion exchange textile substrates according to the invention makes it possible to:

increase the conductivity of solutions in order to improve electrodialysis separation methods and electrochemical methods;

water softening with optionally a bacteriostatic property;

the manufacture of biological protection masks or clothing with virucidal properties;

electrodeionisation for the production of ultra-pure water or for the demineralisation of molecules after synthesis;

the production of battery separators;

the development of a specific contamination indication material for a given bacterium or virus for diagnostic purposes;

the treatment of industrial effluents and water by means of a continuous or batch exchange method and by means of a hybrid electromembrane method combining ion exchange membranes and ion exchange textile substrates.

(2) Prior Art

According to the prior art, industrial grafting methods by means of a chemical process are known wherein molecules are fixed on the textile substrate to be subsequently functionalised particularly by means of reactions in acid or basic medium. In particular, these methods involve the drawback of having to be performed in organic solution and requiring heating. In addition, these methods do not enable grafting of a large range of functional chemical groups, at least simply and in a modular fashion according to the type of textile substrate.

Furthermore, after grafting, the implementation of known methods involves the problem of the removal of the solvent and non-grafted chemical substance which are contained in the textile substrate, and the problem of the subsequent recycling thereof.

Finally, the production of bipolar textile substrate with the methods according to the prior art does not give satisfaction, particularly with respect to the presence of each of the ion exchange functions on a single face.

SUMMARY OF THE INVENTION

The aim of the invention is to remedy the problems of the prior art by proposing a method for grafting functional chemical groups on a textile substrate which is particularly simple and modular in the implementation thereof, said method also making it possible to obtain quality bipolar textile substrates.

To this end, according to a first aspect, the invention proposes a method for grafting functional chemical groups on a textile substrate, said method envisaging impregnating said substrate with a solution of a functional molecule comprising the functional chemical group and a reactive group in ionising radiation, said solution also comprising a surfactant molecule which is capable of improving the wettability of the textile substrate by said solution, said surfactant molecule comprising at least two types of reactive groups in ionising radiation, said method envisaging applying ionising radiation on the impregnated textile substrate to, by means of a reaction of the reactive groups, graft functional molecules by means of coupling with the surfactant molecules.

According to a second aspect, the invention proposes a textile substrate wherein at least one surface is grafted with functional chemical groups, said grafting being performed by means of coupling with a surfactant molecule using such a method.

According to a third aspect, the invention proposes a battery separator whereon sulphonic groups and phosphoric and/or carboxylic groups are grafted, said grafting being performed by means of coupling with at least one surfactant molecule using such a method.

Other specificities and advantages of the invention will emerge in the description hereinafter of various specific embodiments.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

The invention relates to a method for grafting functional chemical groups on a textile substrate, particularly functional chemical groups capable of exchanging cations or anions with the environment thereof, especially with a medium wherein the textile substrate is arranged.

The method envisages impregnating the textile substrate with a solution of a functional molecule comprising the functional chemical group and a reactive group in ionising radiation. According to the solubility of the functional molecule, the solution comes at least partially in the form of an emulsion.

According to one embodiment, the impregnation is performed by means of padding, the impregnated textile substrate being dried before the application of ionising radiation.

In particular, the reactive groups may comprise an unsaturated bond which, under the effect of ionising radiation, forms a reactive free radical. In examples of embodiments, the reactive groups in ionising radiation are selected in the group comprising hydroxyl, carboxyl, carbonyl, acrylate, methacrylate, allyl, amine, amide, imide, urethane groups.

According to one embodiment, the cation exchange chemical group is selected in the group comprising the sulphonic, carboxylic and phosphoric groups, the cation exchange chemical group being selected in the group comprising the amine and ammonium groups.

For example, the functional molecule is selected in the group comprising sulphoalkyl methacrylates (particularly sulphopropyl methacrylate), carboxylic alkyl acrylates or methacrylates (particularly acrylic acid), phosphoric alkyl methacrylates, ethylene glycol methacrylate phosphate, dialkylamonoalkyl methacrylates (particularly dimethylaminoethyl methacrylate), alkyl trialkyl ammonium methacrylates (particularly acryloxyethyltrimethyl ammonium).

Advantageously with respect to the implementation and the environment, the solvent of the solution is water, for example the functional molecule concentration is between 0.5 and 1 M. In addition, the solution may comprise other agents, particularly for improving the solubility of the molecules and/or the stability of said solution.

In one embodiment, the textile substrate is based on fibres made of synthetic material, particularly polyolefinic, as is frequently required for applications envisaged for grafted textile substrates. For example, the fibres may be made of polypropylene, polyethylene, polyester, polyvinyl alcohol or polytetrafluoroethylene (PTFE), or a mixture of these different fibres.

The substrate may comprise a non-woven lap, for example between 0.2 and 5 mm thick and weighing between 30 and 600 g/m². In an alternative embodiment, the textile substrate may be formed from at least one woven or knitted layer.

The grafting method according to the invention may also be implemented with textiles made of natural fibres, such as cotton or wool, or synthetic fibres, such as viscose or cellulose.

The method envisages, to improve the wettability of the textile substrate by the solution, that said solution also comprises a surfactant molecule. In this way, by improving the affinity between the solution and the fibres of the textile substrate, the method makes it possible to graft textile substrates even if they are based on synthetic fibres displaying a high hydrophobicity.

In particular, the nature and quantity of the surfactant molecules in the solution are envisaged so that the surface tension of the solution is similar to that of the fibres. In this way, the textile substrate may be impregnated with a large volume of solution, so as to increase the density of functional chemical groups which are grafted on the textile substrate.

Furthermore, to prevent the subsequent elimination of the surfactant molecule and improve the grafting of the functional chemical groups, the surfactant molecules used comprise at least two types of reactive groups in ionising radiation, said types possibly being identical or different with respect to each other and identical or different with respect to the functional molecule.

In this way, by applying ionising radiation on the impregnated textile substrate, the reaction of the reactive groups ensures the grafting of the functional molecules by means of coupling with the surfactant molecules. Indeed, the reactions of the reactive groups make it possible to bind the surfactant molecules with the fibres or with each other, and the functional molecules with the surfactant molecules or directly with the fibres. This creates a network between the fibres, the functional molecules and the surfactant molecules which is particularly resistant with respect to chemical and mechanical stress to which the grafted textile substrate will be subjected within the scope of the use thereof.

According to one embodiment, the ionising radiation consists of electron bombardment wherein the power and duration may be modulated to activate the reactive groups optimally.

Furthermore, the grafting method is particularly modular in that the nature of the surfactant molecule may be selected according to the textile substrate, particularly according to the surface tension thereof, whereas the nature of the functional molecule is selected according to the functional chemical group to be grafted.

The surfactant molecule may be difunctional comprising two types of reactive groups, for example the surfactant molecule may be selected in the group comprising diacrylates, particularly polyethylene glycol diacrylates (PEG DA). In particular, with PTFE fibres, PEG600 DA is particularly satisfactory and, with high-density polyethylene fibres, the use of PEG200 DA gives satisfaction.

In an alternative embodiment, the surfactant molecule may be trifunctional comprising three types of reactive groups, for example the surfactant molecule may be selected in the group comprising triacrylates, particularly ethoxylated trimethylolpropane triacrylates. In particular, with polypropylene fibres, ethoxylated trimethylolpropane triacrylate 20 is particularly suitable.

After applying the ionising radiation, the textile substrate may be washed and dried or undergo other treatments necessary for the subsequent use thereof. In addition, before grafting, the textile substrate may undergo specific treatments, particularly to improve the cohesion and/or wettability thereof.

According to one embodiment, the solution comprises two functional molecules each comprising a different functional chemical group, the application of the ionising radiation being arranged to graft each of the functional chemical groups on one face of the textile substrate, respectively. In particular, the method is arranged to graft the textile substrate on a defined depth so as to form a superficial layer of grafted material.

In this way, a textile substrate is obtained, comprising two faces which are each grafted with a different functional chemical group. In particular, the textile substrate may have one anion exchange face and one cation exchange face.

For this purpose, ionising radiation is applied on each of the faces, with a penetration thickness of said radiation which is less than the thickness of the textile substrate. In particular, the application of the radiation may be performed in a passage on each side of the textile substrate and the power of the ionising radiation is modulated to obtain the suitable penetration thickness. For example, the textile substrate may be grafted on one half of the thickness thereof with anion exchange groups, and on the other half with cation exchange groups.

In one specific envisaged application, the grafting method makes it possible to produce a battery separator comprising a textile substrate, particularly formed from a synthetic fibre non-woven lap, whereon sulphonic groups and phosphoric and/or carboxylic groups are grafted. In this way, the grafting is performed by means of coupling with at least one surfactant molecule as described above.

In particular, the battery is of the nickel metal hydride type which displays good energy performances but has the drawback of generating ammonium ions during recharging/discharging cycles. However, ammonium ions pollute electrodes and, therefore, the battery recharging level. In this way, the battery autonomy is diminished.

The battery separator according to the invention is characterised in that it includes:

via the sulphonic groups, a battery power improvement function by improving conductivity;

via the phosphoric and/or carboxylic groups, the capture function of the ammonium ions which are produced during the electrochemical operation of the battery. 

1-17. (canceled)
 18. A method for grafting functional chemical groups on a textile substrate, said method comprising the steps of impregnating said textile substrate with a solution of a functional molecule comprising a functional chemical group and a reactive group in ionising radiation, and a surfactant molecule which is capable of improving the wettability of the textile substrate by said solution, which surfactant molecule comprises at least two types of reactive groups in ionising radiation, and applying ionising radiation on the impregnated textile substrate to graft functional molecules by means of coupling with the surfactant molecules and by means of a reaction of the reactive groups.
 19. The grafting method according to claim 18, further comprising basing the textile substrate on synthetic material fibres.
 20. The grafting method according to claim 18, providing a solvent which is water.
 21. The grafting method according to claim 18, further comprising providing said solution with a functional chemical group capable of exchanging cations or anions.
 22. The grafting method according to claim 21, further comprising selecting the cation exchange chemical group from the group consisting of sulphonic, carboxylic, and phosphoric groups, and the amine and ammonium groups.
 23. The grafting method according to claim 22, further comprising selecting the functional molecule from the group consisting of sulphoalkyl methacrylates, carboxylic alkyl acrylates or methacrylates, phosphoric alkyl methacrylates, ethylene glycol methacrylate phosphate, dialkylamonoalkyl methacrylates, and alkyl trialkyl ammonium methacrylates.
 24. The grafting method according to claim 18, further comprising providing the solution with two functional molecules each comprising a different functional chemical group, and arranging the ionising radiation applying step to graft each of the functional chemical groups on one face of the textile substrate, respectively.
 25. The grafting method according to claim 24, wherein said ionising radiation applying step comprises applying ionising radiation on each of the faces, with a penetration thickness of said radiation which is less than the thickness of the textile substrate.
 26. The grafting method according to claim 18, further comprising selecting the reactive groups in ionising radiation from the group consisting of hydroxyl, carboxyl, carbonyl, acrylate, methacrylate, allyl, amine, amide, imide, and urethane groups.
 27. The grafting method according to claim 26, further comprising selecting the surfactant molecule from the group consisting of diacrylates, polyethylene glycol diacrylates (PEG DA), triacrylates, ethoxylated trimethylolpropane triacrylates.
 28. The grafting method according to claim 18, wherein the impregnating step is performed by means of padding, with the impregnated textile substrate being dried before the application of ionising radiation.
 29. The grafting method according to claim 18, wherein said ionising radiation step comprises electron bombardment.
 30. A textile substrate wherein at least one surface is grafted with functional chemical groups, said grafting being performed by means of coupling with a surfactant molecule using a method according to claim
 18. 31. The textile substrate according to claim 30, wherein said substrate is based on synthetic material fibres.
 32. The textile substrate according to claim 30, wherein the functional chemical group is capable of exchanging cations or anions.
 33. The textile substrate according to claim 30, wherein said substrate comprises two faces which are each grafted with a different functional chemical group.
 34. A battery separator comprising a textile substrate whereon sulphonic groups and phosphoric and/or carboxylic groups are grafted, said grafting being performed by means of coupling with at least one surfactant molecule using a method according to claim
 18. 